In the molybdenum wire drawing process, graphite emulsion is used to be coated on the molybdenum wire surface. After drying, the graphite emulsion coating forms a protective layer and high temperature lubricant (prevent the Metal oxide of the molybdenum wire surface in the drawing process). Therefore, the wire surface has a mixture layer of carbon and molybdenum oxide, which can be divided into different chemical structures from surface to metal substrate roughly: Carbon→Carbon+molybdenum oxide→molybdenum oxide→molybdenum.
The impurities of carbon and molybdenum oxide on the molybdenum wire surface will affect the following production and the quality of final products seriously. For example, when the molybdenum wire is used for the energy-saving filament, if the carbon exists on the surface, carbon and molybdenum will react and occur the molybdenum carbide at high temperature, it will not only lead to the brittle fracture of molybdenum wire, but also damage the tungsten wire around the core line. And it will strongly influence the service life of the lamp if the tungsten filament is sealed in the lamp, which contaminated with carbon and oxygen. Therefore, the layer of impurities on the surface, such as the carbon, molybdenum oxide and so on must be removed prior to using. The prior art for molybdenum wire surface be cleaned by electrolytic methods. The wire will be cleaned continuous at electrolyzer. The graphite, the molybdenum oxide and a few molybdenum metal will be dissolved into the electrolytic near the anode and the gas is released near the cathode between a set of electrodes.
The electrolytic cleaning has the following disadvantage:
1. The corrosive gases are occurred in the process of electrolytic cleaning, which will corrupt the equipment and other facilities nearby, endanger the health of the operator, and pollute the atmospheric environment.
2. The cost is very high for the treatment of the waste electrolytic liquid, and the emissions will pollute the surrounding water system even after diluted.
3. Carbon and molybdenum oxides on the wire surface be removed by electrolytic cleaning, but it is inevitable to lead to the molybdenum metal on the surface be dissolving into the electrolyte and cause molybdenum losses.
4. The method can not eliminate the processing stress of molybdenum wire drawing process.
In addition, in order to ensure the accuracy of the product, before the electrolytic cleaning of the molybdenum wire, sometimes a separate stress relief annealing is needed. It will not only extend the production cycle, but also increases production costs.